Tissue separation cannula with dissection probe and method

ABSTRACT

A cannula includes a tubular body having a proximal end and distal blunt end, at least one lumen extending the length of the body, an endoscope having a lighted, viewing end disposed in the lumen near the distal end of the body, and a transparent, tissue-separating tip substantially covering the distal end of the body. The tissue-separating tip is slightly blunted to inhibit avulsion of tissue and lateral vessels along the dissected cavity formed thereby. Endoscopic viewing through the tip is enhanced by tapering the inner walls thereof to a cusp adjacent the blunt tip in order to reduce visual distortion. Alternatively, a cannula includes a dissection probe and a removable or deflectable tip for exposing the probe and endoscope to facilitate viewing and the dissection of connective tissue and lateral vessels along the dissected cavity. Methods of using such cannulas produce an elongated cavity along the course of a blood vessel for subsequent harvesting or other treatment of the isolated blood vessel. The dissection probe includes a partial ring that is substantially coaxially aligned with the generally cylindrical body of the cannula for passing along the vessel and past lateral branching vessels, and that is manipulatable at the distal end of the cannula in view of the endoscope which visualizes through the transparent tip. Where the vessel is an artery, an initial incision is made, for example, above the superior epigastric artery and the overlying tissue is bluntly dissected down to the superior epigastric artery to establish an initial portion of an elongated working cavity of bluntly-dissected tissue. Lateral arterial branches are doubly clipped or otherwise doubly occluded, and then severed to isolate the artery for use in revascularizing the coronary artery, for example, by transection of the superior epigastric or internal mammary artery and attachment of the transected end to the coronary artery downstream of a significant stenotic occlusion.

BACKGROUND OF THE INVENTION

1. Related Application

This continuation of application Ser. No. 08/593,533 filed on Jan. 24,1996, abandoned, which is a continuation-in-part application ofapplication Ser. No. 08/502,494 entitled, "TISSUE SEPARATION CANNULA ANDMETHOD" filed on Jul. 13, 1995, still pending by Albert K. Chin.

2. Field of the Invention

The present invention relates generally to a tissue separation cannulaused for forming an elongated cavity in tissue planes particularly alongthe course of a small blood vessel, and more specifically relates to acannula having an endoscope for continuously visualizing the bluntdissection site through a tissue separating member which is transparentand has a tapered shape and is selectively removable from the cannula tofacilitate dissection of tissue adjacent a blood vessel.

3. Description of Background Art

Present methods for the formation of an elongated cavity involve the useof blunt probes that are pushed through body tissue to accomplish thetissue dissection. The force exerted by the passage of mechanical probesmay lead to blood vessel avulsion and trauma to tissue and internalorgans.

The problem becomes acute when dissecting and harvesting blood vesselshaving a small diameter of about 3 to 8 mm. The techniques which areused for dissection of larger blood vessels such as the aorta are notapplicable since the aorta is located in the retroperitoneum, bounded bythe peritoneum on one side and the psoas muscle on the other side. Aneverting balloon placed in the infrarenal space located just below thekidney will track easily down the length of the aorta along a naturalcleavage plane when inflated.

An everting type of balloon encounters difficulties when dissectingtissue adjacent a smaller-diameter vessel. This is due to the presenceof less distinct planes that exist between small diameter blood vesselsand the tissue that surrounds these vessels, as compared with the aortaand the tissue that surrounds the aorta. For example, if an evertingballoon is placed adjacent to the saphenous vein in the leg, it usuallyskews dissection upon inflation rather than track along the vein. Thisis due to the amorphous nature of the fat and connective tissue thatsurrounds the saphenous vein.

Everting balloon catheters are known which are used for arterialdilation. (See, for example, U.S. Pat. No. 4,479,497 (Fogarty et al.,Oct. 30, 1984) and U.S. Pat. No. 4,863,440 (Chin, Sep. 5, 1989)).

Double lumen everting balloon catheters, such as those disclosed in theFogarty et al. '497 and the Chin '440 patents, have a through-lumen thatslidably receives an endoscope. However, an endoscope used inconjunction with those disclosed catheters is unable to monitor thedissection process, since the endoscope lies within the central lumenproximal to the everting balloon. As the balloon everts from thecatheter, the internal inflation pressure squeezes the walls of theballoon and closes off the distal viewing channel. Also, the area thatrequires monitoring during balloon dissection is located at theadvancing front of the everting balloon. This area corresponds to theballoon/tissue interface that is subject to forces which cause tissueseparation. Thus, an endoscope in the central lumen of existingdouble-lumen, everting balloon catheters is unable to view the area oftissue separation, since a double layer of balloon membrane lies betweenthe endoscope and the tissue and blocks the endoscopic line of sight.This double layer obscures and distorts the viewing area of tissueseparation.

Endoscopes have been disclosed for use in optical trocars such as inU.S. Pat. No. 5,385,572 (Nobles et al., Jan. 31, 1995) and EP 0 642 764A1 (Sauer et al., published Mar. 15, 1995) and in harvesting bloodvessels such as in U.S. Pat. No. 5,373,840 (Knighton, Dec. 20, 1994).The Nobles et a. '572 patent and the Sauer et al. '764 applicationdisclose the use of sharp-tipped, metal cutting elements which extendoutwardly from an endoscope positioned in the trocar. Control of thedissection is difficult because visualization of the vessel is obscuredby the collapse of the tissue planes into the area between the cuttingelement and the endoscope. Furthermore, the risk of side vessel avulsionor trauma to the vessel is greatly increased by the orientation of theoutwardly extending cutting elements.

The endoscope disclosed in Knighton '840 has a lateral dimension of asize sufficient to accommodate the blood vessel being harvested and atleast one tool for use in harvesting the blood harvested. However, thefailure of the endoscope to enlarge a cavity adjacent the blood vesselobscures viewing of the dissection area and manipulation of the vesseltherein. The position of the viewing image relative to the tissuedissection area could obscure the identification of side vessels leadingto an increased risk of vessel avulsion. Since the vessel is retrievedthrough the center of the endoscope, all side vessels must be severedfor the endoscope to advance and the length of the vessel thus retrievedis limited substantially by the length of the body of the endoscope.

An instrument for penetrating body tissue, as disclosed in U.S. Pat. No.5,271,380 (Riek, et al.), is equipped with a tapered tip of transparentmaterial for viewing tissue penetrated by the tip using an optical unitwhich is positioned behind the tip. An instrument of this type mayinclude a separate illumination channel that ends at the tip forilluminating tissue being penetrated.

SUMMARY OF THE INVENTION

The present invention provides a cannula for bluntly dissecting anelongated cavity in tissue particularly along the course of a vessel ina human or animal body. The cannula includes a tubular body havingproximal closed end and distal blunt end and at least one lumenextending the length of the body. The cannula also includes an endoscopehaving a lighted, viewing end disposed in the lumen near the distal endof the body, and includes a transparent, tissue separating member, orblunt tip, substantially covering and selectively removable from thedistal end of the body. The tissue separating member or blunt tipdisposed on the distal end of the body includes internal walls thattaper to a cusp to reduce visual distortion through the endoscope thatis optically aligned with the tip.

A method is also disclosed for bluntly dissecting an elongated cavityparticularly along the course of a vessel using a cannula. The methodincludes the steps of: bluntly dissecting an initial cavity; separatingthe tissue by advancing the cannula along the cavity with continuous,visual observation; repeating the prior step of separating the tissue atleast until the cavity is sufficiently elongated to advance a balloontherein; and successively inflating and deflating a balloon within thecavity to enlarge the cavity along the course of the vessel. Followingdissection of the cavity along the vessel, a counterincision is made atthe far end of the cavity, for example, to place a second blunt tipballoon trocar and to allow introduction of dissection instruments. Thetip of the cannula is advanced out of the body through thecounterincision, and the tapered tip is detached leaving the cannulabody in the dissected cavity. The endoscope resides inside the cannulabody, and the endoscope and cannula body are selectively positioned as asingle unit inside the dissected cavity to facilitate isolating andharvesting the vessel. The method further may include removing thecannula, then maintaining the elongated cavity using insuflated gasthrough a balloon cannula that seals the incisions against gas leakage,or using a structural balloon, or a mechanical structural support withinthe dissected cavity.

In another embodiment of the present invention, the method includes thesteps of bluntly dissecting an initial cavity; sealing and inflating thecavity; and separating the tissue along the cavity assisted bycontinuous, visual observation while under inflation until the cavity issufficiently elongated.

The isolated vessel, such as the saphenous vein, may be harvested andremoved for use as a coronary artery or peripheral vascular bypassgraft, or may be left in place as an in-situ femoropopliteal orfemoral-distal graft. The side branches of the vein are ligated,clipped, or occluded in both applications. In the case of an in-situgraft, the valves in the vein are disrupted by means of a valvulotome.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, longitudinal cross-sectional view of a cannula ofthe present invention illustrating the profile of a tissue separatingmember affixed thereto;

FIG. 2 is an isolated, cross-sectional view of another embodiment of thetissue separating member having a blunt spherical tip with a straighttapered section suitable for use with the cannula of the presentinvention;

FIG. 3 is an isolated, cross-sectional view of another embodiment of thetissue separating member having a blunt tip with a curved taperedsection suitable for use with the cannula of the present invention;

FIG. 4 is an isolated, cross-sectional view of another embodiment of thetissue separating member having a hemispherical shape suitable for usewith the cannula of the present invention;

FIG. 5 is a flowchart of one embodiment of the method of separatingtissue using the cannula of the present invention;

FIG. 6 is a flowchart of another embodiment of the method of theseparating tissue;

FIG. 7 is a partial side view of a patient's leg with the advancement ofa flexible cannula of the present invention through an incision;

FIGS. 8A AND 8B are partial side sectional views showing alternativeembodiments of detachable blunt tips positioned at the distal end of thecannula;

FIGS. 9A AND 9B are pictorial side views showing, respectively,assembled and dissembled configurations of another alternativeembodiment of the present invention;

FIG. 10 is a cross sectional view of cannula of FIGS. 9A and 9B;

FIGS. 11A, 11B and 11C are, respectively, side and sectional views of analternate dissection probe that may be used with the cannula shown inFIGS. 9A and 9B;

FIGS. 11D and 11E are end views of the dissection probe in orbitalpositions about the cannula body;

FIGS. 12A, 12B and 12C are, respectively, simplified anatomical sidesectional and front sectional views of the human body;

FIGS. 13A and 13B are side views illustrating, respectively, retractedand extended configurations of another embodiment of the tissueseparating cannula of the present invention;

FIG. 14 is a partial pictorial view of a viewing, multiple-clip applierfor use in the method of the present invention;

FIG. 15 is a flow chart of an artery isolating procedure according tothe present invention;

FIG. 16 is a flow chart illustrating the procedures involved with thecannula of FIGS. 9A and 9B; and

FIG. 17 is a flow chart illustrating the procedures involved with thecannula of FIGS. 13A and 133.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with one embodiment of the present invention, a cannulaincludes a tubular body having proximal closed end and distal blunt end,at least one lumen extending the length of the body, an endoscope havinga lighted, viewing end disposed in the lumen near the distal end of thebody, and a transparent, tissue separating member substantially coveringthe distal end of the body and selectively removable from the distalend. The present invention also includes methods for using such acannula for separating tissue to form an elongated cavity along thecourse of a small blood vessel and subsequently harvesting the bloodvessel, or using the blood vessel as an in-situ graft.

FIG. 1 shows an embodiment of the cannula 100 of the present invention.The cannula 100 includes a tubular body 102 having a proximal end 104and a distal end 106. At least one lumen 108 extends the length of thebody 102. Disposed in the lumen 108 is an endoscope 110 having alighted, viewing end 112 near the distal end 106 of the body. The otherend of the cannula 100 has a proximal end cap 114 and an elastomericwasher 116 that provides a pressure-sealed, sliding fit with theendoscope 110.

The cannula 100 also includes a transparent, tissue separating member orblunt tip 118 substantially covering the distal end 106 of the body. Thetissue separating member 118 has a tapered section 120 which anglestoward a blunt, tissue-separating tip 122 distal to the distal end 106of the tubular body. The shape of the tissue separating member 118allows atraumatic dissection of a cavity with sufficient control andmaneuverability to prevent tearing or puncturing of the nearby vessel.Typically, the tip 122 has an outer radius of curvature of about 0.030"to about 0.100", and preferably of about 0.045". The length of thetapered section 120 of the tip is approximately 0.500" in length. Thetapered shape and blunt tip of the tissue separating member 118 thusallows deflection of branch vessels to the side of the cannula 100without their avulsion, upon forward advancement of the cannula 100 withreduced requirement of applied axial force to advance the cannula andtip through tissue being dissected.

In tapers of uniform wall thickness with a rounded inner surface nearthe apex, it has been found that a small circular spot of distortionexists in the center of the visual field of the endoscope, equivalent tothe diameter of the rounded taper tip. This distortion may besubstantially eliminated by forming the transparent taper with an innerprofile that ends in a sharp point, or apex, while maintaining the outerprofile as a rounded tip with approximately a 0.045" radius. Undistortedvisual imaging through such tip thus allows the surgeon to track downthe vessel, identify side branches, and guide the device past the sidebranches. An optimal taper length of approximately 0.5" facilitatescannula manipulation around side branches, and the preferredconfiguration of the tapered tip is illustrated in FIGS. 8A and 8B. Thisgeometry greatly improves the imaging of a vessel which lies in contactwith the outer surface of the tapered tip during a surgical procedure toharvest the vessel. The surgeon relies upon the visual images obtainedthrough the tip to guide the tip past side branches without injuringthem along the length of the vessel, such as a saphenous vein, as it isdissected from surrounding fat. The visual images include very subtle"swirl"-like patterns at the center of the image corresponding to whereside branches of the vessels being harvested lie against the distal endof the tapered tip, and such swirl patterns may be readily obscured byoptical obstructions within the field of view through a tip ofconventional configuration.

Alternative embodiments of the present invention include other shapesfor the tissue separating member 118 which provide the necessary controland atraumatic dissection. FIG. 2 illustrates another embodiment of atissue separating member 218 which substantially covers the distal end106 of the cannula and provides a transparent shield for the endoscope110. The tissue separating member 218 includes a tapered section 220integrally formed with a more blunt, spherical section 224 at the distaltip 222 of the tissue separating member.

FIG. 3 illustrates another embodiment of a tissue separating member 318which substantially covers the distal end 106 of the cannula andprovides a transparent shield for the endoscope 110. The tissueseparating member 318 includes a curved tapered section 320 integrallyformed with a blunt section 324 at the distal tip 322 to form aduck-bill shape. The curved tapered section 320 can have convex orconcave shape.

FIG. 4 illustrates another embodiment of a tissue separating member 418which substantially covers the distal end 106 of the cannula andprovides a transparent shield for the endoscope 110. The tissueseparating member 418 has a hemispherical shape 424 covering the distalend 106.

Preferably, the tissue separating members 118, 218 have an overalllength of about 0.5 inches and a uniform wall thickness of about 0.06inches along the entire surface to allow visualization by the endoscopewithout distortion of the image that would result if a section of thewall is thickened or otherwise forms a lens. The wall thickness of thetissue separating member may be contoured to form a lens for specialapplications that require a magnified or otherwise distorted image, e.g.asymmetric, fish-eyed image, or the like, transmitted by the endoscope.Suitable materials for making the tissue separating member or blunt tipinclude polycarbonate and any material which is sufficiently strong toseparate tissue and sufficiently transparent to allow visualization bythe endoscope. As illustrated in FIGS. 8A, 8B, 9A, and 9B, the tissueseparating member or blunt tip may be attached by threads orbayonet-type twist lock to the cannula for selective removal duringprocedures later described herein.

Referring again to FIG. 1, the cannula 100 preferably includes a balloon124 located at the distal end 106 on the exterior wall 126 of thecannula. The balloon 124 may be elastic or inelastic, although anelastomeric balloon is preferred because it achieves a smaller, smootherouter profile. Fully inflated (as shown in phantom 128 in FIGS. 1, 8A,and 8B), the diameter of the balloon 124 is about 3 cm. Preferably, asleeve type of balloon 124 has both the distal end 129 and proximal end130 of the balloon secured to the exterior wall 126 of the cannula.

The balloon 124 is selectively inflated by supplying thereto via anotherlumen 132 a pressurized fluid, such as a gas or liquid, from aninflation port 134 to a hole 136 in the exterior wall 126 of the cannulabetween the proximal and distal ends 129, 130 of the balloon tocommunicate with the interior thereof. A plunger device, such as amanually-operated syringe, is suitable for connecting at the inflationport 134 to control the inflation of the balloon 124. The lumen 132 isformed as another tubular body 138 in a concentric arrangement with thebody 102 to form a space 140 between the two bodies. Another embodimentsuitable of the present invention may include two lumens 108, 132 in aside-by-side arrangement. Additional lumens can be added in similarmanner to provide other functions such as irrigation and aspiration inknown manner.

The present invention is illustrated using a sleeve type of balloon withthe cannula 100. Other balloon types are suitable for use with thepresent invention such as, and not limited to, using an invertableballoon positioned in a separate lumen in the cannula to assist inseparating the tissue when inflated.

The cannula 100 may be manufactured from a variety of bioinert,substantially inelastic materials, such as stainless steel,polyethylene, polyurethane, polyvinyl chloride, polyimide plastic, andthe like that preferably have a tensile strength of at least 10,000 psi.Preferably, each lumen of the cannula 100 has a wall thickness ofbetween about 0.005 inch and 0.010 inch.

The endoscope 110 has an outer diameter of approximately 5.0 mm and anendoscope may be permanently built into the cannula 100, or may be aseparate device that is advanced through the endoscope lumen 108, forexample, through a sliding gas-tight seal 805 configured as shown inFIG. 8A in conventional manner. The endoscope 110 is positioned withinthe lumen 108 with the tip in correct position to allow unimpededvisualization through the transparent blunt tip of the surroundingtissue and vessel outside of the cannula 100. A preferred endoscope 110having a tubular diameter of about 5.0 mm is commercially available fromSolos Endoscopy, Inc., at Norcross, Ga., although othercommercially-available endoscopes 110 as small as 1.00 to 1.75 mm indiameter may also be used.

Methods for bluntly dissecting an elongated cavity using the cannula ofthe present invention are shown in the flow diagrams of FIGS. 5 and 6.Although the blunt dissection of an elongated cavity along the course ofa vessel is specifically described, the present invention is generallysuitable for separating any tissue. For example, the cannula may be usedto track along the median nerve from an incision at the patient's wrist,forming a cavity for surgical treatment of carpal tunnel syndrome. Thecannula allows visualization and tracking of the median nerve,preventing the injury to the nerve which may occur if blind advancementof a balloon cannula were used. Alternatively, the cannula of thepresent invention may also be used to dissect a cavity adjacent themammary artery in the manner as later described herein.

The method illustrated in the flow diagram of FIG. 5 includes the stepsof incising the skin and bluntly dissecting 501 through the subcutaneoustissue to the level of the selected vessel or nerve. Blunt dissection isperformed to separate the vessel from adjacent tissue for a length ofapproximately 1 to 2 cm. The blunt dissection may be performed with apair of curved Metzenbaum scissors, using the tips of the scissors tocut and bluntly spread tissue in a plane between the vessel and theadjacent tissue.

Preferably, a blunt tip balloon cannula is introduced into the spacebetween the vessel and the overlying tissue. The balloon is theninflated to form a gastight seal which seals 502 the dissection. A gassuch as carbon dioxide is infused under pressure via another lumen inthe cannula having an external opening positioned distal to the balloon.The natural perivascular plane around the vessel is expanded by theinjected gas, forming a tract along the course of the vessel. For asuperficial vessel such as the saphenous vein, the expanded tract isvisible on the surface of the skin. The interior of the expanded tractis not cleanly open but rather, includes gossamer-like strands ofconnective tissue and fat, preventing unobstructed visualization andmaking hazardous the passage of an endoscope along the tract adjacent tothe vessel. If a conventional endoscope is pushed into this connectivetissue in an attempt to form a cavity adjacent to the vessel, the viewthrough the conventional endoscope is blurred by the tissue thatcontacts the viewing end of the conventional endoscope. A blurred viewthrough the conventional endoscope increases the potential for sidebranch avulsion during blunt dissection of the perivascular tunnel.

The cannula 100 is inserted 503 into this dissected space. With thefiberoptic endoscope 110 continuously visualizing down the course of thevessel, the cannula 100 separates the tissue by advancing forward 504,probing between the vessel and the adjacent gossamer perivascular tissuein the plane initiated by blunt dissection. The transparent, tissueseparating member 118 allows the endoscope 110 to clearly visualize asegment of the vessel at least equivalent to the length of the taperedsection 120.

If the blunt dissection along the course of the vessel is not sufficientto advance the balloon 124 therein, the method returns 505 to the stepof advancing the cannula 504 forward to continue the separation oftissue along the course of the vessel. When a cavity of sufficientlength has been formed by the cannula 100, the balloon 124 issuccessively inflated and deflated 506 to enlarge the cavity to about 3cm in diameter.

The method returns 507 to the step of separating the tissue by advancingthe cannula 504 and the step of selectively inflating and deflating 506the balloon 124, as described above. Successive application of thesesteps forms a cavity along the entire length of the vessel. Once theelongated cavity is complete, the cannula 100 is completely retracted508 from the elongated cavity.

The elongated cavity site is then maintained 509 in expanded form inaccordance with the method of the present invention. Following use ofthe cannula 100 to form an elongated cavity along the course of avessel, the cavity must be supported to allow procedures to be performedon the vessel, such as vessel dissection, grafting of the vessel, orvessel harvesting. A blunt tip trocar may be used to seal the entranceincision and allow gas insufflation to maintain the cavity in expandedform. One blunt-tip balloon trocar suitable for use herein is presentlymarketed by Origin Medsystems, Inc. of Merilo Park, Calif.

Another method of maintaining the cavity in expanded form includesmaking an incision at the distal extent of the dissected cavity, andinserting a double rod system through the cavity. The double rods aresuspended via a laparoscopic mechanical lifting device to maintain thecavity. This system allows instruments to be advanced into the cavityvia simple incisions, without the requirement for trocars with gassealing valves, as is the case with gas insufflation.

Alternatively, an inflatable structural balloon or mechanical structuremay be used to support the dissected cavity. For example, the cavity maybe maintained by mechanical retraction or by a mechanical finger-likeretractor attached to a powered lifting arm plus a separate flat balloonretractor used to displace the side wall of the cavity. The endoscope110 may be introduced behind the legs of the finger-like retractor thatconnect to the mechanical lifting arm.

The vessel is completely dissected within the formed cavity, usinglaparoscopic instruments such as graspers, scissors, hooks, and bluntprobes. Side branches to the vessel may be ligated using suture ties,clipped using titanium vessel clips, cauterized using electrocautery, ora combination of these procedures. The dissected vessel is removed fromthe cavity for possible use as a conduit for an arterial bypassprocedure, or the vessel may be left in place to be used as an in-situbypass graft.

In an alternate embodiment, the method of the present invention forms asmall diameter cavity, about 7 mm, along the entire length of the vesselbefore the cavity is then enlarged. As illustrated in FIG. 5, the stepsof making a blunt dissection 501, sealing and inflating the dissection502, inserting 503 the dissection cannula 100 and successivelyseparating the tissue by advancing 504 the cannula 100 are performed asdescribed above. The alternate method, however, continues advancing 504the dissection cannula until the entire length of the elongated cavityis bluntly dissected to the small diameter of about 7 mm.

Only after the entire length of the elongated cavity has been bluntlydissected does the alternate method include the step of inflating anddeflating 506 the balloon 124 of the cannula to increase the diameter ofthe distal end of the elongated cavity to about 3 cm. The dissectioncannula 100 is then retracted 508 partially by about the length of theballoon 124. The alternate method then returns 510 to the steps ofinflating and deflating 506 the balloon 124. The cannula 100 is againretracted 508 partially and the method returns 510 to repeating theabove steps until the entire length of the elongated cavity has beenenlarged to the diameter of the inflated balloon 124 which is typicallyabout 3 cm.

An alternate method involves making an incision down to the vessel.Blunt dissection of the vessel from the adjacent tissue is performed fora 3-4 cm length. A blunt tip trocar is placed in the incision, and gasinsufflation is initiated.

The cannula 100 is inserted through the blunt tip trocar, and bluntdissection using the balloon 124 is performed under the presence of gasinsufflation in the cavity. This technique provides a larger cavity forvisualization during separation of the tissue, since gas insufflation isused from the onset of blunt dissection. However, a gas sealing blunttip trocar is required. If vessel dissection without gas insufflation isconducted, and a double rod system is used to maintain the cavity, thenthe use of a blunt tip trocar may be avoided.

Another method of the present invention forms a small diameter cavityalong the entire length of the vessel. The cavity is enlarged only bythe initial inflation at the blunt dissection site. As illustrated inFIG. 6, the steps of making a blunt dissection 601, sealing andinflating the dissection 602, inserting 603 the cannula 100, andsuccessively separating the tissue by advancing 604 the cannula 100 areperformed as described above. The cannula advances 604 until the entirelength of the elongated cavity is bluntly dissected and expanded only bythe inflating gas of the prior step 602. The cannula 100 is thenretracted 605 entirely from the elongated cavity. The dissection site ismaintained 606 in expanded form as described above.

The present invention includes methods particularly useful forharvesting vein. In one method, an incision is made near the ankle, andthe cannula is passed along the sophenous vein up to the knee, or nearthe knee. Following balloon inflation to enlarge this segment, anincision is made into the dilated cavity near its endpoint at the knee.The incision at the knee is the approximate mid-point of the saphenousvein between the ankle and the groin. The vein is isolated and the sidebranches ligated in this segment between the ankle and the knee toharvest and remove this segment.

The segment from the knee to the groin is then harvested. The cannulamay be passed from the same knee incision used for harvesting the veinfrom the lower leg, or a separate incision down to the vein may be madeslightly above the knee. Use of a separate incision may be useful if thevein is overly curved or tortuous as it passes around the knee. Thecannula is advanced toward the groin, the balloon is inflated to dilatethe cavity, an incision is made into the dilated cavity at its groinend, and the portion of the saphenous vein residing in the thigh isharvested.

As an alternate method for saphenous vein harvesting, the initialincision may be made at the knee. The cannula is passed successively inboth directions, toward the ankle and toward the groin, from the sameincision. Then additional incisions are made at the ankle and at thegroin to allow harvesting of the entire length of the saphenous vein.The vein may be removed as a single strand, or it may be cut at the kneeand removed as two strands.

In some anatomic regions, it may be difficult to advance a rigid,straight tissue separation device along the course of a vessel. Forexample and referring to FIG. 7, if the saphenous vein 700 is harvestedby passing the cannula 702 from an incision 712 just above the ankle,the presence of the medial malleolus 704 and the foot 706 may prevent anotherwise rigid cannula from being angled upwards or sideways to followthe vein 700.

For such obstructed situations, the cannula 702 may be formed with abody which is flexible or otherwise malleable, or is rigid with apre-determined gradual arc, as shown in FIG. 7. The endoscope 708 thatis inserted into the cannula 702 up to the tissue separating member 710must also be flexible to facilitate shaping the flexible body within thecurved cannula. Such conventional flexible fiberoptic endoscopes arecommercially available for use in gastrointestinal endoscopy.

In other embodiments of the method, and of the apparatus illustrated inFIGS. 8A and 8B, the tapered and transparent tip 803 of the cannula 800may be removably attached to the body of the cannula. At the cannulainsertion site, a blunt tip balloon trocar (for example, as commerciallyavailable from Origin Medsystems, Inc.) is placed to seal an incisionand allow insufflation into the space to be dissected by the cannula 800which is advanced through the blunt tip trocar along the course of thevessel. The balloon on the cannula is selectively inflated to dissect aperivascular cavity. Following dissection of the cavity along thevessel, a counterincision is made at the far end of the cavity to placea second blunt tip balloon trocar and allow introduction of dissectioninstruments. The tip of the cannula is advanced out of the body throughthe counterincision and the tapered tip 803 is detached, leaving thecannula body in the dissected cavity. The endoscope resides inside thecannula body, and the endoscope/cannula body is advanced as a singleunit inside the working cavity to isolate and harvest the vessel.

The detachable tip 803 may be attached to the cannula body 800 using athreaded connection between the tip and the distal end of the cannulabody, or a bayonet-type of fitting my be used to lock the tip onto thecannula, with a slot in the tip engaging a pin on the end of the cannulabody.

The cannula of this embodiment with a detachable tip 803 has theadvantages compared with the embodiment of the cannula described withreference to FIG. 1 that the 5 mm diameter endoscope used with thecannula often does not have sufficient rigidity to allow it to bedirected along the dissected working cavity for unobstructedvisualization. For example, in the lower leg, the curvature of the calfmuscle impedes visualization along the surgical cavity, and theendoscope must deflect muscle tissue to allow it to view down the boreof the cavity. Flexion of the endoscope which is about 45 cm long andabout 5 mm diameter may prevent successful visualization. The cannulawhich surrounds the endoscope according to the present invention has an8 mm outer diameter, and this larger diameter imparts rigidity to theendoscope/cannula system. The cannula body may be constructed ofstainless steel for additional rigidity.

Also, the ability to remove the tapered tip 803 via an incision at theopposite end of the cavity results in a decreased number of passes ofthe cannula and endoscope up and down the length of the cavity. Thisadds to the convenience of the procedure, and decreases the potentialfor vessel injury by decreasing the number of full length passesrequired through the dissected cavity.

Referring now to FIGS. 9A and 9B, retracted and dissembledconfigurations of another embodiment of the cannula 900 of the presentinvention are illustrated. Specifically, the outer body of the cannula900 includes a sleeve-type balloon 901 secured to the body at proximaland distal ends thereof, as illustrated in FIGS. 8A and 8B, forselective inflation via a lumen 1010 within the body that communicatestherewith, as illustrated in the sectional view of FIG. 10.

At the distal end of the body of the cannula 900, a detachable,transparent blunt tip 903 is shown in FIG. 9A retracted onto the distalend of the cannula body, and is shown in FIG. 9B mounted on push rod 906and extended beyond the distal end of the cannula body 900 to expose theviewing end 905 of an endoscope, and a crescent-shaped dissection probe907. The probe 907 is mounted on shaft 909 to facilitate selectivemanipulation of the dissection probe 907 within the field of view of theendoscope 905. As shown in FIG. 10, the push rod 906 may be non-circularwithin a mating non-circular lumen to retain the blunt-tip 83 in axialalignment as it is selectively extended and retracted relative to thedistal end of the cannula body 900. Also as shown in FIG. 10, the shaft909 for supporting the dissection probe 907 may be circular orcylindrical to facilitate both longitudinal and rotational positioningof the dissection probe 907 via corresponding manipulations of the shaft909 at the proximal end of the cannula body 900. Alternatively, theshafts 906 and 909 may reside in slots of suitable sectional shapesalong the outer surface of the cannula body 900, with an encirclingsheath of heat-shrinkable PET plastic, or other bioinert plastic, toretain the shafts 906, 909 in captivated orientation along the cannulabody 900.

The dissection probe 907 has leading and trailing edges thereof tofacilitate selective dissection of strands of connective tissue andlateral branch vessels along the saphenous vein, or other vessel, to beharvested. The blunt tip 903 may thus be selectively extended beyond thecannula body 903 (or the cannula body 900 may be retracted relative tothe tip 903) to expose the dissection probe 907 at a selected locationalong a dissected cavity adjacent a vessel being harvested. Selectivetranslational and rotational manipulations may be achieved via similarmanipulations of the shaft 909 at the proximal end thereof to dissectconnective tissues and lateral branch vessels along the course of thevessel being harvested. The dissection probe 907 and the blunt tip 903may then be retracted into axial alignment with the cannula body 900, asshown in the retracted configuration of FIG. 9A. Surgical proceduresinvolving the cannula 900 of FIG. 9A are described later herein withreference to the flow chart of FIG. 16.

Referring to the side and sectional views of FIGS. 11A, 11B, and 11C,the dissection probe may be formed in separate, spiral-like segments1101, 1103 that are axially spaced along the supporting shaft 909, forexample, in the illustrated configuration, to provide greaterconvenience in selectively by-passing or dissecting connective tissueand lateral branch vessels along the course of a vessel being harvested.Thus, as shown in FIGS. 11D and 11E, the dissection probe 907 (or 1101and 1103) may be orbited about the axis of shaft 909, and the cannulabody 900 may be rotated on its longitudinal axis to facilitate thedissection of the vessel away from connecting tissue, and the traversalof side-branch vessels.

Referring now to FIGS. 12A and 12B, the simplified side and frontalillustrations of the human anatomy disclose another operatingenvironment for the apparatus and method of the present invention, forexample, in preparing the internal mammary artery for coronary arterybypass. Specifically, the combined blunt tip cannula and dissectionprobe of the present invention permits a working cavity to be formedalong a vessel, and the vessel to be dissected and isolated, orotherwise manipulated as later described herein, via a single incision.This decreases the number of incisions required to harvest a vessel. Thecannula and dissection probe of the present invention facilitateharvesting the internal mammary artery in the chest wall to enable itsuse as a coronary artery bypass graft. The internal mammary artery maybe harvested via a single subxiphoid incision, with the rectus musclebluntly dissected to expose the superior epigastric artery. The cannulatracks along the superior epigastric artery which leads directly to theinternal mammary artery that lies behind the ribs lateral to thesternum. The internal mammary artery is dissected substantially in themanner as previously described up to its origin at the subclavianartery. Its side branches are clipped and transected, and distally, itis transected to yield a free end which is anastomosed to the coronaryartery to complete the bypass.

As illustrated in FIGS. 12A, 12B and 12C, the internal mammary artery(also known as the internal thoracic artery) runs internal to the costalcartilages, lateral to the sternum, descending to the interval betweenthe sixth and seventh cartilages where it bifurcates into the superiorepigastric artery and the musculophrenic artery. The superior epigastricartery lies within the rectus sheath. In its superior portion, it liesbehind the rectus abdominis muscle. The superior epigastric arteryeventually anastomoses with the inferior epigastric artery.

Since the superior epigastric artery lies in the abdominal wall withinthe rectus sheath, it may be easily found, for example, using Dopplerultrasound, and isolated via incision of the skin and blunt spreading ofthe rectus abdominis muscle overlying the artery. The blunt tip, visualballoon dissection cannula previously described herein may be placednext to the isolated section of superior epigastric artery, and passedsuperiorly, following the course of the superior epigastric artery toits junction with the internal mammary artery. An endoscopic workingcavity may be formed along the length of the internal mammary artery inthe manner previously, described herein, allowing side branchidentification and interruption, and using vessel clips or bipolarelectrocautery closure followed by scissor transection. The dissectedportion of the internal mammary artery may then be used to revascularizediseased coronary arteries, facilitated by the availability of theendoscopic working cavity thus formed along the internal mammary artery.

This abdominal approach to internal mammary artery dissection ispreferable to a supraclavicular approach or an intercostal approachsince the supraclavicular approach is impeded by the presence of thesubclavian artery and the aortic arch, and dissection risks trauma tothese vessels. In contrast, the intercostal approach gives limitedexposure, unless rib spreaders are used, and only a small portion of theinternal mammary artery is accessible from the side. The abdominalapproach described herein thus allows the entire length of the internalmammary artery to be exposed. By initiating the dissection at the levelof the superior epigastric artery, no vascular or bony structures arepresent to impede the passage of the dissection cannula of the presentinvention, thereby resulting in a safer approach to the internal mammaryartery.

Specifically, with reference to the flow chart of FIG. 15, the method ofcreating a working space along the superior epigastric artery accordingto the present invention includes forming an incision 1501 of the skinand blunt dissection 1503 and spreading of the rectus abdominus muscleoverlying the artery. The balloon cannula as illustrated in FIGS. 1, or8A, 8B, or 9A, 9B, 13A, 13B is inserted in the bluntly dissected cavitynext to the isolated section of the superior epigastric artery. Thecannula is advanced 1505 along the course of the superior epigastricartery and the internal mammary artery by the iterative sequence ofadvancing the cannula, visualizing dissection of tissue through thetransparent tip until resistance to tissue penetration is felt. Theballoon is inflated to expand the cavity around the cannula adjacent theartery, and then deflated, and the cannula is again advanced, andretracted and diverted and advanced as required to properly track thecourse of the vessel substantially to its junction with the subclavianartery. The tunnel or cavity thus formed along the artery facilitatesside branch identifications for subsequent operative procedures, and inone embodiment of the process invention the cannula may be completelyremoved 1507 from the working cavity thus formed by successivelyinflating and deflating the balloon to establish an adequate workingcavity as the cannula is completely withdrawn therefrom.

Next, the artery may be dissected from the cavity wall by placing 1509 ablunt tip trocar in the working cavity at the abdominal incision, andthe associated balloon is then inflated. The cannula of the presentinvention including the dissection probe and an endoscope positioned1511 within a lumen of the cannula is positioned in the working cavitythrough a gas tight port of the trocar, with the dissection probepositioned about the artery. The dissection probe is now translated androtated 1513, as illustrated in FIGS. 11D and 11E to free the arteryfrom connective tissue. The axial opening 908 in the perimeter of thedissection probe facilitates passing over lateral branch vesselsencountered along the course of the artery being isolated. When theartery and side branches are completely free of connecting tissue, thecannula with endoscope and dissection probe is removed 1515 from theworking cavity.

Thereafter, a viewing, multiple-clip applier, as illustrated in FIG. 14,including a clip applier 1401 and an endoscope 1403, and having acircular cross section may be inserted 1517 through the trocar port forplacing two surgical clips on each side branch of the isolated artery1519, spaced sufficiently to divide the branch vessel therebetween.After all side-branch vessels are clipped in this manner, the viewing,multiple-clip applier is completely removed 1521. Alternatively, atwo-port, trocar gas seal may be attached to the blunt tip trocar and anendoscope may be inserted through one port with a clip applier orelectrocauterizer inserted through the other port for clipping orotherwise occluding the side-branch vessels. The two-port seal for theblunt tip trocar facilitates removal of only the clip applier andreplacement thereof by scissor blades that can be manipulated proximallyto cut and divide 1523 each of the side branch vessels between the clipsthat were previously placed or through electrocauterized segment thatwas prepared while viewing through the endoscope 1403. Thereafter, thescissor blades may be removed, and the internal mammary artery thusisolated may then be used to revascularize diseased coronary arteries1525, for example, by grafting a transsected free end of the isolatedinternal mammary artery to the left anterior descending coronary arterydownstream of a significant stenotic occlusion.

Referring now to FIGS. 13A and 13B, there are shown side views ofretracted and extended configurations of another embodiment of thedissection cannula according to the present invention. This embodimentincludes a blunt, tapered tip 1301 which deflects to one side of theendoscope 1303 to allow visualization outside of the cannula 1300 duringvessel dissection and isolation. The dissection probe 1305 may resideadjacent to the cannula body 1300, proximal to the tapered tip 1301, andextend forward to dissect around the vessel being harvested and its sidebranches. The dissection probe shaft 1307 may run through a separatelumen in the cannula body 1300. The cannula body 1300 may contain anintrinsic curvature, and contain a port 1309 on the side of the cannulabody near the tip, for exit of the endoscope 1303. The cannula bodywhich has a normally curved configuration, straightens out uponintroduction of a rigid, straight endoscope 1303. Partial retraction ofthe endoscope 1303 allows the cannula to curve, and the endoscope isadvanced through the side port 1309 in the cannula body 1300 to viewoutside of the deflected cannula tip 1301.

A surgical procedure involving the cannula 1300 shown in FIG. 13 isillustrated in the flow chart of FIG. 17. Specifically, an initialincision and blunt dissection is performed 1701 to prepare an initialdissected cavity. The cavity may then be sealed 1703 in conventionalmanner and inflated 1705 to facilitate insertion of the cannula 1300that is inserted into the cavity 1707 through a conventional gas-tightseal. The cannula is advanced 1709 and a perimeter balloon 128 on thecannula is inflated 1711 to expand the dissected cavity, and is thendeflated to facilitate further advancement of the cannula andreinflation of the balloon. This sequence is repeated 1712, 1713 untilthe dissected cavity of sufficient size or length is formed along thevessel of interest. The dissected cavity is maintained 1715 byinsufflation or mechanical traction or otherwise, as previouslydescribed, and the cannula may be retracted 1717 to a selected locationin the cavity at which the endoscope 1303 may be retracted 1719 relativeto the body of the cannula 1300 in order to permit deflection of theblunt tip 1301 away from the tip of the endoscope, as shown in FIG. 13B.Thereafter, the endoscope 1303 may be extended 1721 to view past theblunt tip 1301, and the dissection probe 1305 may also be extended 1723and manipulated within the dissected cavity to dissect the vessel ofinterest 1725 from remaining connective tissue.

Referring now to the flow chart of FIG. 16, a surgical procedureinvolving the cannula 900 shown in FIG. 9A includes making an initialincision and blunt dissection 1601 to form an initial dissected cavity.The cavity may then be sealed 1603 in conventional manner and inflated1605 to facilitate insertion 1607 of the cannula 900 into the cavitythrough a conventional gas-tight seal. The cannula 900 is advanced 1609and a perimeter balloon 901 on the cannula is inflated 1611 to expandthe dissected cavity, and is deflated to facilitate further advancementof the cannula, and reinflation of the balloon. This sequence isrepeated 1612, 1613 until the dissected cavity of sufficient size orlength is formed along the vessel of interest. The dissected cavity ismaintained 1615 in a manner as previously described, and the cannula 900may be retracted 1617 sufficiently within the dissected cavity tofacilitate detaching and/or extending 1619 the blunt tip 903 andfacilitating extension 1621 of the dissection probe 907. One or more ofthe steps 1617, 1619, and 1621 may be repeated while dissectingconnecting tissue 1623 to harvest the vessel of interest.

Therefore, the cannulas and dissection probes and associated surgicalprocedures facilitate blunt dissection of a working cavity along avessel of interest, with visualization of the tissue being dissectedthrough a blunt tip of transparent material and selected opticalconfiguration positioned on the forward end of the cannula. Selectiveremote deployment and remote manipulation of a dissection probe carriedon the cannula facilitates dissection of tissue around the vessel ofinterest and around side branch vessels along the vessel of interestbeing harvested from within and along the working cavity of dissectedtissue.

I claim:
 1. A cannula for dissecting an elongated cavity in tissueparticularly along a course of a vessel, the cannula comprising:atubular body having a proximal end and a distal end; at least one, lumenextending within the length of the body; an endoscope having a lighted,viewing end disposed within the lumen near the distal end of the body; atransparent tissue separating member substantially covering the distalend of the body and having a conically tapered outer surface convergingtoward a blunt tip disposed toward of the distal end of the body fordirectory contacting tissue, the member having substantially rigid andnon-collapsible walls and having an internal surface that converges to asharp point at a location substantially aligned with the viewing end ofthe endoscope for visualization thereby with reduced distortion throughthe walls of the member; and a balloon attached to an exterior wall ofthe tubular body of the cannula near the distal end of the tubular bodyat a location thereon that is remote from the outer surface of themember for selective inflation and deflation of the balloon in responseto fluid pressurization thereof through a lumen extending within thetubular body without obstructing visualization through the member viathe endoscope by the inflated or deflated balloon.
 2. A cannulaaccording to claim 1 in which the outer surface of the tissue separatingmember forms a tapered outer surface converging toward a blunt tiphaving a radius of curvature substantially in the range of fromapproximately 0.030 inches to approximately 0.100 inches.
 3. A cannulaaccording to claim 2 in which the outer surface of the tissue separatingmember forms a blunt tip having a radius of curvature of approximately0.045 inches.
 4. A cannula according to claim 1 including a dissectionprobe mounted on a shaft disposed in the body for movement of the probenear the distal end thereof in response to manual manipulation of theshaft near the proximal end of the body.
 5. A cannula according to claim4 in which the dissection probe includes a crescent shaped memberdisposed on the shaft in substantially concentric orientation with thebody for selective movement relative to the distal end of the body forsevering tissue thereabout.
 6. A cannula according to claim 4 in whichtho dissection probe includes at least one partially circular elementdisposed on the shaft in substantially concentric orientation with thebody for selective movement relative to the distal end of the body forsevering tissue thereabout.
 7. A cannula according to claim 1 in whichthe conically tapered outer surface to the blunt tip is about 0.5 inchesin length.
 8. A cannula according to claim 1 in which the dimension ofthe member at the distal end of the tubular body is about 8 millimeters.9. A cannula for dissecting an elongated cavity in tissue particularlyalong a coarse of a vessel, the cannula comprising:a tubular body havinga proximal end and a distal end; at least one lumen extending within thelength of the body; an endoscope having a lighted, viewing end disposedwithin the lumen near the distal end of the body; a transparent tissueseparating member substantially covering the distal end of the body andhaving a conically tapered outer surface converging toward a blunt tipdisposed forward of the distal end of the body for directly contactingtissue, the member having substantially rigid and non-collapsible wallsand having an internal surface that converges to a sharp point at alocation substantially aligned with the viewing end of the endoscope forvisualization thereby with reduced-distortion through the walls of themember and the member being selectively displaceable from the distal endof the body.
 10. A cannula according to claim 9 in which the tissueseparating member rotatably attaches to the distal end of the body forselective rotational detachment of the member from the body.
 11. Acannula according to claim 9 in which the member as supported on a shaftmounted in the body for selective movement thereof relative to the bodyfor selectively positioning the member remote from the distal end of thebody.
 12. A cannula according to claim 11 in which the member assupported on the shaft for translational movement thereof relative tothe distal end of the body in response to manipulation of the shaft nearthe proximal end of the body.
 13. A cannula according to claim 11including a dissection probe mounted within the body for selectivemovement relative thereto and far exposure upon movement of the memberrelative to the distal end of the body.
 14. A cannula according to claim13 including the dissection probe and the member mounted on shaftsoriented along the length of the body to the proximal end thereof tofacilitate manual manipulation thereof for selectively moving the probeand member relative to the distal end of the body.
 15. A cannulaaccording to claim 4 comprising:a balloon attached to an exterior wallof the tubular body of the cannula near the distal end of the tubularbody at a location thereon that is remote from the outer surface of themember for selective inflation and deflation of the balloon in responseto fluid pressurization thereof through a lumen extending within thetubular body without obstructing visualization through the member viathe endoscope by the inflated or deflated balloon.
 16. A cannula fordissecting an elongated cavity in tissue particularly along a course ofa vessel, the cannula comprising:a tubular body having a proximal endand a distal end and a portion that is laterally deflectable, andincluding a port near the distal end of the body; a least one lumenextending within the length of the body; an endoscope having a lighted,viewing end disposed within the lumen new the distal end of the body,the endoscope being slidably disposed within the lumen within the bodyfor selectably emerging from the port in response to lateral detectionof the body; a transparent tissue separating member substantiallycovering the distal end of the body and having a conically tapered outersurface converging toward a blunt tip disposed forward of the distal endof the body, the member being substantially rigid and non-collapsibleand having an internal surface that converges sharp point at a locationsubstantially aligned with the viewing end of the endoscope.
 17. Acannula according to claim 16 including a dissection probe mounted formovement relative to the body and being disposed therein to emerge fromthe port distal of the endoscope in response to lateral deflection ofthe body.
 18. A cannula for dissecting an elongated cavity in tissueparticularly along a course of a vessel, the cannula comprising:atubular body having a proximal end and a distal end and including a portnear the distal end of the body; at least one lumen extending within thelength of the body; an endoscope slidably disposed within the lumen andhating a lighted, viewing end disposed within the lumen near the distalend of the body for selectively emerging form the part in response tolateral deflection of the body; a transparent tissue separating membersubstantially covering the distant end of the body and having taperedouter surfaces converging toward a blunt tip disposed forward of thedistal end of the body, the member being substantially rigid andnon-collapsible and having an internal surface that converges to a sharppoint at a location substantially aligned with the viewing end of theendoscope for visualization thereby through the member with reduceddistortion, and the member being selectively displaceable from theviewing end of the endoscope near the distal end of the body in responseto lateral deflection of the body.